1. Field of the Invention
The present invention relates to an automatic compensation circuit for use with a linear displacement type sensor which dynamically compensates for errors in the sensor output signal based upon ideal values stored in electronic memory.
2. Description of the Prior Art
Various linear type displacement sensors, such as angular position sensors, are known to be used for various purposes including throttle position sensors for determining the angular position of a butterfly valve in a throttle body. Examples of such sensors are disclosed in U.S. Pat. Nos. 4,893,502 and 5,332,965. Such sensors are generally used to control the amount of fuel applied to the combustion chamber of an internal combustion engine.
Such throttle position sensors, such as the sensors disclosed in U.S. Pat. Nos. 4,893,502 and 5,332,956, are typically subject to part-to-part variations which require each and every sensor to be calibrated either by the throttle body manufacturer as in the case of U.S. Pat. No. 4,893,502 or the sensor manufacturer as in the case of U.S. Pat. No. 5,332,965. In the embodiment disclosed in the '502 patent, a circular magnet is rigidly secured directly to the butterfly valve shaft. A magnetic resistive element (MRE) is disposed within a modified throttle body at a fixed air gap relative to the circular magnet. An amplifying circuit with variable gain is used to calibrate the sensor by way of potentiometers or variable resistors.
As is known in the art, the output of such potentiometers may vary with temperature or time. Due to the relatively wide operating temperature range of such a sensor used in an internal combustion engine environment, such potentiometers will drift and affect the overall calibration of the device. The sensor disclosed in the '965 patent is mechanically adjusted; and thus, the calibration is not subject to drift as in the case of the '502 patent. However, such mechanical adjustments are time-consuming and cumbersome, which increases the overall labor cost to manufacture the product.